In general, a solid polymer electrolyte fuel cell (PEFC) includes a unit cell (unit power generation cell) configured by oppositely disposing an anode and a cathode, each of which is mainly made from carbon, on both sides of an electrolyte membrane of a polymer ion exchange membrane (cation exchange membrane), to form a unified body (membrane-electrode assembly), and holding the unified body between separators (bipolar plates). The solid polymer electrolyte fuel cell is generally used as a fuel cell stack having a specific number of the unit cells.
In the fuel cell of this type, when a fuel gas, for example, a gas mainly containing hydrogen (hereinafter, referred to as “hydrogen containing gas”) is supplied to the anode, hydrogen in the hydrogen containing gas is ionized on the catalyst electrode and is migrated to the cathode side via the electrolyte; and electrons generated by such electrochemical reaction are taken to an external circuit, to be used as electric energy in the form of a direct current. In this case, since an oxidizing gas, for example, a gas mainly containing oxygen or air (hereinafter, referred to as “oxygen containing gas”) is supplied to the cathode, hydrogen ions, electrons and oxygen react with each other to produce water on the cathode.
When a fuel cell stack is used as an on-vehicle power source, a relatively large output is required for the fuel cell stack. To meet such a requirement, a cell structure for making a size of a reaction plate (power generation plane) of a unit cell larger, and a cell structure for stacking a large number of unit cells to each other have been adopted.
The former cell structure, however, has a problem that the enlarged size of each unit cell leads to the enlargement of the whole size of the fuel cell stack and such a large-sized fuel cell stack is unsuitable as an on-vehicle power source. Accordingly, to obtain a relatively large output, the latter structure for stacking a large number of relatively compact unit cells to each other has been generally adopted. However, as the number of the stacked unit cells becomes larger, the temperature distribution tends to be generated in the stacking direction and also the drainage characteristic of water produced by the electrochemical reaction is degraded, thereby failing to ensure a desired power generation performance.
To solve the above-described problems, the present invention has been made, and an object of the present invention is to provide a solid polymer electrolyte fuel cell assembly capable of effectively improving the power generation performance of each unit cell and reducing the size of the cell assembly with a simple structure, and a fuel cell stack composed of a stack of the cell assemblies.
Another object of the present invention is to provide a method of supplying a reaction gas in a fuel cell, which allows effective power generation of each unit cell and also allows improvement of the drainage characteristic of produced water.